If you have a large enough container you may be able to trap the poor piggies and at least get them inside and safe until you can contact the owner again.

Take a large container and make some holes at the bottom (so that it won't flood if the rain starts up again) and line it with a towel or similar, something nice and cozy. Put some food (they seemed to like the carrots before, try that) in the bottom and then make a "ladder" leading up into the container. Put the whole lot on your yard as close to where the piggies are known to hang out as you can, and check on it every so often.

The idea is that they will climb up the ladder to get to the food, fall into the container and not be able to get back out, a sort of pit trap really. The same thing will work on a smaller scale with other escaped animals, e.g. hamsters. (Which is how i learned it, lol)

After that, personally I would bring them inside, make sure they were healthy and go speak with the occupier/owner of the place, ask if they still wanted the guineas and if not, take them on as you've already said you're interested in doing that.

If you're not comfortable with trapping them maybe you could make them a little shelter, a cardboard box on a couple of bricks with some shredded paper, a water bowl and maybe some food inside. Stick a tarp or cut open plastic sack over the top to keep off the rain. At least they'll be comfy.

If you don't catch them, i'd call the spca. They are in danger and need helping, evidently their owners aren't caring for them as they should be.

This is not safe for the piggies. You returned them when they moved in and they aren't interested in containing them, you rang the doorbell when they were home and they weren't interested.

Just take the piggies and keep them if you want or bring them to the shelter. They need help. They are going to get sick or eaten and it sounds to me like the owners have intentionally "liberated" them.

If you let a guinea pig loose in your yard you should expect it to disappear one way or the other. If they lost them accidentally, they would be looking for them, have food out, have talked to neighbors, etc. I lost a cat the day we moved here and I had visited all the neighbors by the next day, and I slept with my phone near me for 6 weeks until he showed up about a mile away and they called for me to go get him.

If they ask you about them at some point, I would just say that you took them in so they'd be safe. But I suspect they will not ask or look for them. Poor piggies.

Update:I waited until I saw the neighbours outside (yesterday) and approached the man I was quite certain was the homeowner. I let him know that I had spotted both guinea pigs under the bushes, but could not catch them and didn't want to trespass.

Due to the language barrier, it was a bit awkward trying to figure out if he understood what I was saying, but I must have gotten the point across and he must have taken it seriously/appreciated it.

I saw them pulling up some of the weeds between the bushes to try and catch the piggies. And this morning when I left my house, the bushes were hacked way back to almost nothing. Like, they really went to town in that garden to catch the critters. And there were no guinea pigs to be seen in the front lawn.

I'm still not totally convinced they take really good care of the animals - after all, the piggies were in the front yard for at least 2 days and there was no sign of the neighbours looking for them. But they aren't there now, so I think all I can do is hope that they are being cared for.

I noticed a few people suggesting that you call the ASPCA. A lot of people don't realize that the ASPCA is NOT affiliated with their local SPCA. They only run one shelter - and that happens to be in NYC, so unless that is where you live calling them won't do you much good. They do say that they work with groups around the country, and they do that, but for a specific one animal issue like this you are much much better off calling your local animal control. SPCA, or whatever agency handles animal issues in your area. They have a huge back log of cases they are investigating in NYC - their jurisdiction - so calling from across the country is not going to get you quick help - if they can help you at all.

This is just a friendly reminder because a lot of people don't realize the national organizations are not tied with the organizations that use the same name in your area and they waste time calling them when they will just get redirected back to the organization in their own area.